mm/page_alloc.c: fix 'zone_id' may be used uninitialized in this function warning

mainline inclusion
from mainline-v5.15-rc1
commit b346075f
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I4S7MA
CVE: NA

--------------------------------

When compiling with -Werror, cc1 will warn that 'zone_id' may be used
uninitialized in this function warning.

Initialize the zone_id as 0.

Its safe to assume that if the code reaches this point it has at least one
numa node with memory, so no need for an assertion before
init_unavilable_range.

Link: https://lkml.kernel.org/r/20210716210336.1114114-1-npache@redhat.com
Fixes: 122e093c ("mm/page_alloc: fix memory map initialization for descending nodes")
Signed-off-by: NNico Pache <npache@redhat.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: NMa Wupeng <mawupeng1@huawei.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

mm/page_alloc.c

@@ -6510,7 +6510,7 @@ void __init __weak memmap_init(void)
 {
 	unsigned long start_pfn, end_pfn;
 	unsigned long hole_pfn = 0;
-	int i, j, zone_id, nid;
+	int i, j, zone_id = 0, nid;
 
 	for_each_mem_pfn_range(i, MAX_NUMNODES, &start_pfn, &end_pfn, &nid) {
 		struct pglist_data *node = NODE_DATA(nid);